1. Field of the Invention
The present invention relates to an optical information recording reproduction device for recording signals on an optical recording medium with laser light.
2. Description of the Related Technology
Recording of information on optical recording media such as optical disks is performed in such a manner that record data is modulated by Eight to Fourteen Modulation (EFM) or Eight to Sixteen Modulation; a recording pulse is formed according to the modulation signals; the intensity and radiation timing of laser light are controlled according to the recording pulse; and thus recording pits are formed on the optical recording media.
For such optical information recording, an object lens with a large numerical aperture (NA) is effective in recording and reproducing data to/from high-density mass-storage recording media. However, the allowable variations of the laser-beam spot diameter are extremely small for the high-density mass-storage recording media and the manufacturing tolerances of optical recording media and optical pickups (thickness and warping for media, lens tilt etc. for pickups) are also significantly reduced.
A known optical information recording reproduction device adopts a method of allowing variations in spot diameter by determining the spot diameter of the laser light radiated on an optical recording medium from the level of RF signals and reading the optimum strategy for the spot from a strategy table stored in a memory and recording it (Method for Controlling Optical Disk Recording and Reproduction Device disclosed in JP-A-2006-85842).
The tolerance of optical recording media and optical pickups causes the problem of aberration. Means for reducing the aberration includes a method for preventing aberration in such a manner that a first negative lens and a second positive lens are arranged in sequence behind a collimating lens, wherein when the substrate of an optical recording medium is increased in thickness, the distance on the optical axis between the first negative lens and the second positive lens is reduced, and when the substrate of the optical recoding medium is decreased in thickness, the distance on the optical axis between the first negative lens and the second positive lens is increased (Object Lens System Variable with Thickness of Disk Substrate disclosed in JP-A-9-197264 by Mark KK) and a method for reducing aberration by changing the distance between an object lens and an attachment lens according to the thickness of the substrate of an optical recoding medium using a pickup having the attachment lens (Apparatus and Method for Recording and Reproducing Data to/from Recording Medium disclosed in JP-A-9-251662 by Sony Corp.).
Requirements for high-recording-quality optical disk recording reproduction devices are optimization of the spot diameter of a laser beam applied on a recording medium, selection of strategy optimized for laser beam spots and the recording medium, and prevention of aberration caused by tolerance.
However, “Method for Controlling Optical Disk Recording and Reproduction Device” disclosed in JP-A-2006-85842 by SANYO Electric Co. Ltd. does not cope with the aberration, although it optimizes the strategy for laser beam spots. “Object Lens System Variable with Thickness of Disk Substrate” disclosed in JP-A-9-197264 by Mark KK does not refer to a method for determining aberration, although it shows means for correcting aberration.
“Apparatus and Method for Recording and Reproducing Data to/from Recording Medium” disclosed in JP-A-9-251662 by Sony Corp. shows a method for determining the thickness of the substrate of a recording medium by detecting a focus error (FE) signal, although it may be difficult to separate the influence of defocusing from the influence of the thickness of the substrate of the recording medium.
Accordingly, it is desirable to provide an optical information recording reproduction device capable of stable aberration detection for achieving high recording quality.